Lab I-DNA Structure

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Georgia College & State University *

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2100

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Biology

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Jan 9, 2024

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docx

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Lab Activity Name _Kaylin Carter_ Complete this activity individually to maintain social distancing, but feel free to discuss it with your lab partner and work on each step together, checking your models with each other to make sure you’re on the same page. You will each complete and hand-in your own lab. It will be due by our next lab meeting. II. Nucleotides and Complementary Base-pairing. Use your textbook as a resource to explore the models. Observe two disassembled nucleotides . Please do not mark on the models. 1. What do the colors of the atoms represent? Hydrogen = white, yellow = phosphorus, red = oxygen, blue = nitrogen, gray = carbon 2. Identify the phosphates, deoxyriboses and nitrogenous bases. Locate the various carbons of deoxyribose (e.g., which is the 5’, which is the 3’). Do you have two purines, two pyrimidines, or one of each? One of each 3. Assemble your two individual nucleotides. Find the 5’ and 3’-end of the nucleotides. Base-pairing. Observe two more nucleotides. 1. Create a G-C and an A-T base-pair. These are known as the two Watson-Crick base-pairs. How do they differ? How are they the same? G-C base pairs have 3 hydrogen bonds while A-T have 2. Both base pairs have one purine and one pyrimidine. 2. Note how the hydrogen bond acceptors/donors are involved in each base-pair. 3. Are these base-pairs antiparallel or parallel? antiparallel 4. Non-Watson Crick base-pairs. A-T and C-G are known as Watson-Crick base-pairs, other pairings are possible and these are known as non-Watson-Crick base-pairs.
What are all ten possible unique base-pair combinations? Complete the series in the first column of the table below. 5. Populate the table below for these ten base-pair combinations and in the columns to the right enter additional information you will now discover by assembling the base- pairs. As needed obtain additional nucleotides. Use the model to test out each of these pairings and determine the following: in the second column record if the hydrogen base-pairing of a combination (e.g. A-A) is parallel or antiparallel (if both are possible, pick the one that results in more hydrogen bonds); record the number of hydrogen bonds that can occur in its strongest form; indicate if the base-pair type is it is a purine-purine (R-R), pyrimidine:pyrimidine (Y-Y), or purine:pyrimidine (R- Y). base-pair parallel or antiparallel? # of hydrogen bonds (strongest pairing) base-pair type (R- R, R-Y, or Y-Y) A-G parallel 2 Y-Y A-C antiparallel 2 Y-R A-T antiparallel 2 Y-R A-A parallel 2 R-R C-G antiparallel 3 R-Y G-G parallel 2 R-R T-C antiparallel 2 Y-Y T-G parallel 2 R-Y T-T parallel 2 Y-Y C-C parallel 2 Y-Y 6. Compare the width of Watson-Crick base-pairs to non-Watson-Crick base-pairs that allow antiparallel hydrogen bonding disrupt a B-DNA double helix? What is meant by “pinch” and “bulge?” A pinch is when 2 pyrimidines bond to each which makes it less than 2 nm wide and a bulge is when 2 purines bond together, which is more than 2 nm wide. In Watson and Crick base pairing, DNA is 2 nm wide.
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